Bone formation results from a complex set of anabolic and catabolic processes regulated by endocrine, paracrine, and autocrine factors. Precursor cells are recruited into the osteoblast lineage and stimulated to produce an organic network of collagen fibrils, forming a substrate for mineral salt deposition. This organic/inorganic matrix ossifies and becomes subject to catabolism by other resident bone cells. Therefore, bone formation is dynamic and must be maintained throughout life. Whereas many growth promoters are found associated with the bone matrix, it is particularly enriched with transforming growth factor beta (TGF beta). TGF beta stimulates both osteoblastic bone cell replication and subsequent collagen production, but by apparently unrelated processes. The effect on collagen production seems to be mediated at multiple levels of control. The purpose of the proposed research is to dissect the effect of TGF beta on bone cell collagen production at the molecular level. Specifically, the synthesis and half-life of collagen mRNA in osteoblast-enriched cell cultures will be examined by molecular hybridization studies using the cDNA probe to rat type I collagen. The relationship between collagen mRNA and collagen polypeptide production will be studied in cell-free extracts prepared from these cultures. The extracts will be used to examine the association of collagen mRNA into protein synthesis initiation complexes by hybridization and specific filter binding assays, and the entry of collagen mRNA into polyribosomes by velocity sedimentation analysis. Collagen production and turnover rates will be measured by collagen specific proteinase assays, by collagen breakdown product analysis, and by polyacrylamide gel analysis. Understanding the effect of TGF beta on the molecular level may produce new insights into the role of this potent local bone growth factor in metabolic bone disease and functional repair after fracture. Results from these studies may also provide different and rational approaches in detection and treatment of disorders in bone development, remodeling, and repair.